Method of producing cellulose and paper from straw, esparto, reed, and similar raw materials



Patented June 4, 1929.

1,716,006 PATENT oFFl'cE.

UNITED STATES ERIK LUDVIG RINMAN, 0F DJ'UIRSHGLM, SWEDEN.

METHOD OF PRODUCING CELLULOSE AND PAPER FROM STBAW, ESPARTO, REED, AND SIMILAR RAW MATERIALS.

No Drawing. Application filed March 28, 1927, Serial No. 179,195, anc1 in Sweden April 7, 1926.

Cellulose made from straw has hitherto been used exclusively as an ingredient added to other cellulose in the manufacture of line grades of note-paper and writing-paper. 1n the production of such cellulose the main object has been to obtain an easily washed and easily bleached cellulose, and for this purpose the straw has been boiled at an excess )ressure of t to 6 kg. per sq. cm. The cellulose fibre obtained in this manner, however, becomes short and weak. During recent times another method has also been pro posed which consists in first treating the straw at a low temperature of about 100 C.

' with caustic soda lye, so that a half stall is obtained which is afterwards transformed into cellulose by treatment with chlorine, such cellulose being further treated, it desired, by bleaching in the ordinary manner. This latter method, however, gives a still more short-fibred cellulose, for which reason it has a very limited use.

Now, the present invention relates to a method of producing from straw, csparto, reed, and similar raw materials, a cellulose having properties quite different from those of the above-mentioned hitherto known straw cellulose, and also to a method of producing from the cellulose thus obtained, a paper having properties particularly desirable for certain purposes. The method of produc ing the cellulose consists principally in that the raw material is subjected to boiling with caustic soda lye, with or without sodium sulphide added thereto, at a temperature above 100 C. but 'not exceeding 140 0., in such manner that glutinous substances present in the raw material are not destroyed, and that the separation of the waste liquor from the cellulose after the boiling is completed, is carried out at a temperature of C. at the highest, so that theglutinous substances are not dissolved from the cellulose, butmay be utilized in the production of paper from the cellulose obtained. The raw material may consist of ordinary straw, for instance straw or rye, wheat, barley or oats, or of reed, Indian corn straw, rice straw, esparto, sugar cane, sunflower stalks, cotton plants, papyrus, or similar vegetable matter. The separation of the waste liquor from the cellulose fibres is carried out most suitably insuch manner that the entire pulp together with the waste liquor is cooled to about 30 C. before the separation, and that the washing itself is carried out by means of cold wash- 0 ing liquids and cold water. It .is also possible, however, to obtain a good result bv carrymg out the separation of the waste liquor i'ronrthe cellulose in such manner that the principal quantityofwasteliquoris separated at a temperature of about 50 C., after which the washing proper is eli'ccted with washing liquids and washing water of a ten'iperature of 30 C. at the most. The separation of the waste liquor from the cellulose may suitably be efliected by the aid of a rotary filter, since ordinary washing in diil'usors can not be used in this case owing to the presence of the glutinous substances in the cellulose.

From the cellulose produced in this manner-termed straw cellulose here belowwhich contains the glutinous substances present in the rawmaterial used, a great many special grades of papers having desirable properties for particular purposes may be produced by means of ordinary paper machinesj Thus, after grinding the straw cel-. lulose in heaters with lightly adjusted knives so that the cellulose fibres areneither cut on nor torn asunder, a pulp is obtained having a degree of grinding of to 80 degrees Schopper-Riegler from which pulp parchmentpaper or greaseproof paper may be produced on suitable paper machine's. A pulp having a degree of grinding of 05 to degrees S.-R. gives an excellent grease'proot paper, whereas for producing parchment paper the grinding should be carried to 75 to degrees Salt. If it is desired to produce thicker paper, for instance such having a weight of over 50 gr. per sq. 111., it is suitable to heat the cellulose pulp before it is spread outupon the wire apron ot' the paper machine. Such heating should never be carried above 40 C. but may without inconvenience run up to. 30 C. If higher temperatures are used the glutinous substance is easily dissolved, so that the paper produced losesin closeness. The paper produced in this manner becomes perfectly air-tight and, provided that digester liquor tree from sodium sulphide was used for the production of the straw cellulose, it has also the advantage of being absolutely inodorous and free from injurious'acids and inorganic substances.

If the'straw cellulose 'is ground in the manner above described in heaters with lightly adjusted knives but only to a grinding degree of 55 to 60 degrees S.-R., a pulp is obtained which directly gives an. excellent kraft paper having at least an equally great. breaking length and tensibility as the best kraft papers which it has hitherto been possible to produce from sulphate pulp made from wood. If it is desired to increase the power of the paper to resist tearing, one may add to the straw cellulose obtained in the manner above described a suitable quantity of long-fibred pulp, for instance krait pulp, strong sulphite pulp, jute fibres, hemp fibres, or cotton fibres. An addition of 10 percent of any of the three last mentioned kinds of fiber is quite sullicicnt for obtaining an unusually strong kraft paper. Such kraft paper loses very little in strength by being stored, owing to its freedom from lignin, particularly in case no glue has been added.

The straw cellulose obtained in the manner above described may also be used to replace the strong sulphite cellulose in the production of ordinary newsprint paper. The yellow colour of the straw cellulose is scarcely noticeable in the paper owing to the great addition of mechanical pulp (about percent) and may, besides, always be covered by adding suitable dyes. The straw cellulose obtained according to the invention shows on the whole a great resemblance to ordinary sulphite cellulose.

'lhe straw cellulose produced according to the invention may be bleached without the glutinous substance being destroyed, if a higher temperature than about 30 C. is not used during the bleaching. With theuse of the customary bleaching liquids, for instance ordinary solution of chloride of lime, a good bleaching -is attained during a normal time if the bleaching is carried out at a temperature of 25. C. Bleached in this manner the fibres of the pulp lose only very little in strength. From the straw cellulose bleached in this manner one may obtain, by suitable grinding, parchment paper as well as greaseproof paper. Furthermore, such pulp can wholly or partly take the place of bleached sulplnte pulp in the production of line papers of all grades.

In order to illustrate the method an example of the manner in which it may be can ried out is described here below.

Rye straw is used as raw material. The straw is first chopped to chaff of a length of about 3 cm. The chaff is afterwards sifted through a rotary sieve which must be so fine that it does not let through the ears but all chairs. The chopped straw free from cars obtained in this manner is afterwards passed through a cyclone apparatus for the purpose of removing the dust. The chopped straw is afterwards boiled in an upright digester with circulating digester liquor which is drained just below the middle of the digester and,

after having been passed through a heater,'

is again admitted into the upper and lower ends of the digester. For the boiling a mixture of white liquor and black liquor is suitably used, so that when the boiling is finished, the waste liquor has a specific gravity of 1.1% at 20 C. For the boiling 150 to 170 kg. NaOll are used per 1000 kg. chopped straw. The time of boiling amounts to about 3 hours when an excess pressure of 1.8 kg. is used. Yhen the boiling is finished the pulp is blown to a blowing dillusor from which it is tapped into a receptacle in which it is diluted with strong cold black liquor, so that a mixture is obtained which contains about 4 percent cellulose and has a temperature of 50 C. at the most. Afterwards the straw cellulose is separated from the waste liquor by means of a rotary filter on which the washing is etlected, at first with cold washing liquids and linally with cold water. Formation of scum in the rotary filter apparatus receptacle for liquor and washing liquid is suitably prevented by an addition ofpetroleum, or oils having a high boiling temperature and obtained by dry distillation of waste liquor from the cellulose manufacture. For the purpose of washing the straw cellulose difi'usors can not be used, since after cooling the black liquor the pulp can not be filtered in thick layers owing to the presence of the glutinous substances. The pulp obtained is afterwards diluted with water, during further defibration if desired, after which the knots are strained ofi. The pure pulp thus obtained is afterwards ground in heaters in the manner above described, after which it is ready to be transferred on to the wire apron of the paper machine. If the pulp is to be bleached, this may suitably be eifected simultaneously with the defibration, after which the pulp is strained and further treated.

For grinding the pulp heaters having very broad knives may suitably be used. The pulp can then be ground to a grinding degree of 75 degrees S.-R. in two or three hours time without the fibres being torn 03.

I claim:

1. The method of producing cellulose from straw, esparto, reed, and similar raw materials, which consists in subjecting the raw material to boiling with caustic soda lye at a temperature not exceeding 140 C. whereby the glutinous substances present in the raw material are not destroyed but are capable of being utilized in the production of paper.

from the cellulose obtained, and separating the waste liquor from the cellulose after the boiling is completed at a temperature not exceding 50 C. whereby the glutinous substances are not dissolved from the cellulose.

2. In the production of paper from straw, esparto, reed, and similar raw materials, produeing cellulose from the raw material by subjecting the same to boiling with caustic soda lye at a temperature not exceeding 14:0" C. whereby the glutinous substances present in the raw material are not destroyed, separatingthewasteliquors fromthecellulose after the boiling is completed at a temperature not exceeding 50 C. whereby the glutinous substances are not dissolved from the cellulose, and grinding such cellulose in beaters with so loosely adjusted knives that the fibres of the cellulose are only defibrated and hydrated but are not cut up or torn off.

3. In the production of thick parchment paper and greaseproof paper from straw, esparto, reed, and similar raw materials, producing cellulose from the raw material by subjecting the same to boiling with caustic soda lye at a temperature not exceeding 140 C. whereby the glutinous substances present in the raw material are not destroyed separating the waste liquors from the cellulose after the boiling is completed at a temperature not exceeding 50 C. whereby the glutinous substances are not dissolved from the cellulose, grinding such cellulose in beaters with so loosely adjusted knives that the fibres of the cellulose are only defibrated and hydrated but are not cut up or torn off, and heating the cellulose obtained to about 30 C. but not above 40 C. before transferring the same to the wire apron of the paper machine.

ERIK LUDVIG RINMAN. 

